Magnetostrictive materials are used for torque sensors and the like, for example, for detecting torque on the transmission shaft of electric power-assisted bicycles. A torque sensor is usually configured by attaching a thin film of a magnetostrictive material on the surface of the torque transmission shaft. The torque sensor detects deformation of the transmission shaft caused by a rotary torque, from a change in magnetic permeability of the magnetostrictive material deformed by the deformation, and measures the magnitude and direction of the torque. The change in magnetic permeability of the magnetostrictive material is detected from a change in inductance of a solenoid coil disposed so as not to contact the magnetostrictive material.
A study using an amorphous alloy as a magnetostrictive material is known (patent literature 1). The magnetostrictive material has an amorphous structure produced by a single-roll liquid quenching technique and also a microcrystallite precipitated by a thermal process. The properties of the magnetically isotropic amorphous structure, rather than those of the magnetically anisotropic crystalline structure, are used.    Patent Literature 1: Japanese Unexamined Patent Publication No. Hei-7-118786    Patent Literature 2: Japanese Patent No. 3946226    Patent Literature 3: Japanese Unexamined Patent Publication No. Hei-5-149804    Patent Literature 4: Japanese Unexamined Patent Publication No. 2001-41833    Patent Literature 5: Japanese Unexamined Patent Publication No. Hei-10-176966